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New Model Traces Water Pollution Back To Land

The U.S. Geological Survey's SPARROW model pulls together water quality data from the local, state and federal level to identify the primary sources of nutrient pollution in water bodies across the Northwest.

A new computer model from U.S. Geological Survey connects activities on land with water pollution problems in nearby waterways.

SGS Hydrologist Daniel Wise said maps created by the SPARROW model offer a valuable tool for understanding water quality – and possibly improving it.

“We grabbed every piece of water quality data that was available for the Northwest and compiled it for the first time in one place,” Wise said. “It allows us to relate what we see in streams and aquifers to what we see on land. If there’s a large problem here, we can look at: Is that because of fertilizer or point sources? For the first time we have tools to do that.”

So far, the model only includes sources of nutrient pollution: nitrogen and phosphorous that are typically associated with fertilizer runoff and wastewater treatment discharges.

Too much nitrogen and phosphorous in waterways causes excessive plant growth, said Wise, which leads to low dissolved oxygen and conditions that can be harmful to aquatic wildlife.

But the model begins to account for non-point sources of pollution – such as agricultural runoff that isn’t regulated by the Clean Water Act.

For example, to model for nitrogen pollution, USGS looked to land use designations and statewide sales of fertilizer.

In the maps created by the model, you can see where water bodies are listed under the Clean Water Act as “impaired” and cross-reference them with sources of nutrient pollution.

Right now, the model pulls data from 1994 to 2004, but it will be updated next year with newer data.

In the future, it could allow people to check the water quality in their local waterway and identify sources of water pollution, Wise said.

One map he pointed to shows how much phosphorous is running off the land on the west side of the Cascades than on the east side.

“It’s mostly from natural sources – with all that rain,” he said. “On the east side, it’s associated with irrigated agriculture.”

Ideally, he said, government agencies could use the model to test out different regulatory scenarios.

For example, you could run the model on the Tualatin River with less point-source pollution from wastewater treatment plants “to see what difference that makes downstream.”

That could help inform regulators about the best way to clean up impaired waters.

“It could also show that focusing on point sources might not get them to where they want to be,” he said.

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